Resistance unit.



G. DFKNIGHT, P. H. ZIMMBR & J. B. FORD.

RESISTANCE UNIT.

APP IIIIIIIIIIIIII EB. 111111 7.

1,010,641 Patented Dec. 5, 1.911.

- .EYYENTUHS WJTN CH/IHLL 27. KNIGHT.

PAUL Zl/HZYIE'H E I g JUHN E. TURF.

ATTY

UNITED STATES PATENT OFFICE.

CHARLES D. KNIGHT, PAUL H. ZIMMER, AND JOHN B. FORD, OF SCHENECTADY, NEW YORK, ASSIGNORS T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

RESISTANCE UNIT.

To all whom it may concern.-

Be it known that we, CHARLES D. KNIGHT, PAUL H. ZIMMER, and JOHN B. Fono, citizens of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Resistance Units, of which the following is a specification.

This invention relates to resistances to be used in electric circuits, and has for its object the provision of a resistance device or unit which is adapted'for use in a variety of places and under various conditions; being capable of withstanding a high temperature without injury and at the same time being thoroughly reliable in operation and simple and eflicient in construction.

One of the objects of our invention is to produce a resistance unit capable of general use with rheostats and controllers.

It is frequently necessary in the electrical art to providea resistance unit which will stand a considerable rise of temperature without danger of injury to itself or to its surroundings. For this purpose the inclosed or embedded resistances have been proposed, such for instance as the enameled type, in which the resistance wire is secured to and insulated from a metal support by means of enamel. In the case of enamel, however, an exceedingly high temperature is necessary to cause the fusing of the insulating substance. This high temperature injures the conductor and furthermore does not allow for expansion which must necessarily take place when the conductor becomes hot. The enameling process furthermore requires special means for producing and maintaining a high temperature, all of which renders the unit expensive and generally undesirable.

In carrying out our invention we provide a unit in which the resistance conductor is secured to a support by means of a material which will stand an exceedingly high. temperature, but which does not require a high temperature to apply. While it is generally preferable to use an insulating sup port, this is not necessarily so, as we may insulate the conductor from the support by means of the material itself.

In the single figure of drawing we have shown a resistance, unit embodying our invention.

Referring to this drawing, 1 is the sup- I Specification of Letters Patent.

' Application filed February 21, 1907.

Patented Dec. 5, 1911. Serial No. 358,532.

port for the resistance conductor 2. In the unit shown in the drawing, the support is a tube upon which the conductor is wound, although the particular form of'support is no part of our invention. The material of the tube may, of course, be varied at will. We have found it to be very convenient and eflicient to employ a tube of flexible, insulating material, such for instance as asbestos. By using a flexible tube, the conductor sinks into the support to a certain extent and is thereby prevented from displacement, which might short-circuit some of the turns and destroy the unit. This will also give some latitude in which the conductor can adjust itself to Variations of temperature. The asbestos moreover will stand a high temperature without injury and may be obtained at a very low cost. The asbestos tube moreover renders the unit very light, and we consider that the feature of having a yielding tube of this character acting as a support for an inclosed resistance, is a very important one.

As a material for embedding the resistance, many substances may be found useful. Many of the silicates, for instance, have the refractory insulating properties necessary for use in this connection. The mineral silicates, such for instance as silicate of alumina, have been found to be especially desirable as to properties and cost. Feldspar and flint mixed with silicate of soda or waterglass as a binder make a composition which is exceedingly easy to, apply, and which is found to have most desirable properties. By combining these substances in about the following proportions: feldspar 30%, silicate of soda 30%, flint 30% and water 10%, a material is produced which will withstand a temperature at which enamel resistance fails and which is nonhygroscopic. It will not crack or scale either due to the expansion and contraction of the conductor or from outside influence, that is, it will not break if dropped or if struck a blow. As a convenient mode of application, the substance is preferably made to about the consistency of cream, and the resistance which has previously been formed by winding the conductor on the tube is dipped into this substance. The unit is then set away to dry, whereupon the insulating substance forms a hard, thick coating 3 over the conductor. While the insulating material above described will harden if simply left in a dry place at an ordinary temperature, it is preferable to hasten the hardening operation by placing the unit in an oven for a short time, thereby driving ofi the moisture and making a granite-like substance which is practically indestructible.

Units of this character are usually supported at the ends and in order to insure against the grounding of the conductor to the metal frame on which it is mounted, we employ a special insulation at the ends of the unit. The ends are made of a solid, insulating, refractory substance, such for instance as a porcelain insulator 4 which fits into the asbestos tube, and in addition to acting as a solid support, tends to stiflen the tube. We do not mean however to limit our invention to the use of a porcelain insulator since other means of rendering the end of the tube secure against short-circuits and the like may be employed without departing from the spirit of our invention. Other materials may also be employed as an embedding substance, and the support may be altered both as to shape and material without departing from the spirit of our invention, the scope of which is set forth in the annexed claims.

What we claim as new and desire to secure by Letters Patent of the United'States, 1s.--

1. A resistance unit comprising a yielding, insulating tube having refractory and moisture excluding ends, and a resistance conductor wound thereon and embedded in a mineral silicate.

2. A resistance unit comprising a yielding, insulating tube having solid insulating and moisture excluding ends, and a resistance conductor Wound thereon and embedded in a mineral silicate.

3. A resistance unit comprising an asbestos tube provided with porcelain ends, and a resistance conductor wound thereon and embedded in a mineral silicate.

A. A resistance unit comprising an asbestos tube having porcelain insulators inserted in the ends thereof, and a resistance conductor wound into and embedded in a mineral silicate.

In witness whereof, we have hereunto set our hands this 19th day of February, 1907.

CHARLES D. KNIGHT. PAUL H. ZIMMER. JOHN B. FORD.

Witnesses:

HELEN ORFORD, BENJAMIN B. HULL. 

